patch 8.1.1826: tests use hand coded feature and option checks

Problem:    Tests use hand coded feature and option checks.
Solution:   Use the commands from check.vim in more tests.
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index d762c91..5bb601e 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -1,6 +1,7 @@
 " Tests for autocommands
 
 source shared.vim
+source check.vim
 
 func s:cleanup_buffers() abort
   for bnr in range(1, bufnr('$'))
@@ -1861,9 +1862,9 @@
 endfunc
 
 func Test_Changed_FirstTime()
-  if !has('terminal') || has('gui_running')
-    return
-  endif
+  CheckFeature terminal
+  CheckNotGui
+
   " Prepare file for TextChanged event.
   call writefile([''], 'Xchanged.txt')
   let buf = term_start([GetVimProg(), '--clean', '-c', 'set noswapfile'], {'term_rows': 3})